Here We Come(t): Success of the Rosetta Mission

The landing of ESA’s (European Space Agency’s) Philae lander on the comet 67P last week (on November 12th 2014) was reported pretty widely as a “failure”. The primary reason was twofold: the legs that were the landing mechanism for Philae failed to fire; and when it did finally land (using backup mechanism), it landed in a shadow region of the comet. This means that after transmitting for about 26 hours, the probe went silent. It has been so ever since. However, many have called this one of the biggest achievements in space in recent history; and we explain why.

The excitement surrounding the event was considerable, mainly because the “Rosetta” mission, the name of the spacecraft that was orbiting the comet, has been on for 10 years. In 2004, Rosetta was sent to the difficultly named 67P/Churyumov-Gerasimenko comet: to follow it and orbit it until the opportune time when Rosetta could send its probe Philae to land on the comet and study this mysterious celestial phenomenon. So last week was the culmination of 10 years of waiting. After all this, then, the process may not have been exactly foolproof: considering that the entire landing procedure depended on the one nudge Rosetta give Philae when initiating the landing; a nudge masterminded by its controllers on Earth. Philae is a completely automated study device: so there was absolutely no control once it had been released. And if that one release/nudge was botched, the high speeds meant the lander would bounce off the comet and spiral off into space: 10 years of waiting and hard work gone to waste. The release actually worked out fine; but almost everything else went wrong: the mission was inches from failure time and time again. To begin with, the Philae’s main landing mechanism: the “harpoons”, which were meant to fire and attach to the comet as soon as probe was close enough to align the speeds and allow a smooth approach, failed. Instead the probe flew in full speed and crashed into 67P, nearly flying off into deep space on the rebound. Its landing gear (landing legs), which were supposed to kick in even if the harpoons didn’t fire, took one more bounce before gripping the surface in some way. It was a harrowing 1hr 30 minute wait after the first impact before the comet’s gravity was able to pull it back: one landing leg hanging half-outside the probe, still no idea whether the lander would secure. It took another hit; but just seven minutes later came back, and stayed. It was a celebratory moment for the team: first comet landing in history; unfortunately, the bounces meant it was far from the intended touchdown spot. It actually managed to wedge itself somewhere between the giant comet’s cliffs, hidden from the Sun that was meant to power it after the first two days. And so, at the end of all this excitement and effort, Philae lost all contact with Earth: and was unable to continue transmitting the information it had been sent there to collect.

I must admit this sounds quite ominous, but only on the surface. The ESA team actually had no idea, even after touchdown, whether the little craft had been secured until they got their first transmissions from it: which showed all its instruments were working, and somehow what was left of landing gear had managed to anchor the probe. Then, Philae was able to begin collecting data from the comet’s surface and transmitting it: for the next two days, humans got their first look at the surface of a comet, from the surface of a comet. ESA scientists explain that the lander was able to complete its ‘First Science Sequence’: using relatively basic instruments to quite rapidly collect and transmit fascinating, new comet data to Earth. This included information on the interior of the comet from an instrument that sends radio waves inside the comet nucleus, and insights into the geology of the surface from an instrument that studies its chemical composition. From knowing almost nothing about what is actually on and inside a comet about a week ago, the impact this mission might have scientifically is extraordinary. Add that to all the information Rosetta has collected for the past year after it became the first spacecraft to orbit a comet, and you have a mission that cannot be called anything but a success. And although it is in a dark zone, it will still receive some sunlight: maybe enough to perform a few of the more exciting tests and transmit hopefully a little of the data it collects. (Second stage tests include drilling into the surface and more) The ESA scientists haven’t given up on contact from little Philae just yet.

The most important achievement, however, lies beyond the science: the landing of a probe on a comet is huge in itself. We’ve touched a comet before: NASA’s Deep Impact probe achieved a head on collision with comet Temple1 that showed us just a bit of the inside before both flew off in different directions. But achieving a soft landing gave us both the preliminary data that will tell us whether comets can be of any use to us at all, and if yes: the knowledge that we can send rovers and maybe even astronauts in the future. We’ve landed on asteroids, but speeds made comets a much tougher ask: these two may just be the future of humancommerce. We’ve reached moons, planets and asteroids before: comets were mankind’s next giant leaps, and with Philae we have conquered them.